1. Field of the Invention
The present invention relates to a thermally assisted magnetic recording device. More particularly, the present invention relates to a thermally assisted magnetic recording device provided with a means for preventing a thermally assisted magnetic head from colliding with a disk due to thermal deformation of a near-field transducer (NFT), and for keeping the distance constant between the thermally assisted magnetic recording head and the disk.
2. Description of the Related Art
One technique for significantly increasing the recording density of a magnetic disk is called thermally assisted magnetic recording. Thermally assisted magnetic recording is designed to record data onto a disk by applying heat over 200 degrees C. and magnetic field to a micro area of about tens of nm×tens of nm in the disk. One proposed means for heating such a micro area is to convert a laser beam into near-field light by a near-field transducer provided in the vicinity of a main magnetic pole.
However, there is only several percent of the applied laser power in the thermally assisted magnetic recording head that can be converted into the near-field light by the near-field transducer, and can contribute to the heating of the disk. The rest of the laser power is absorbed and converted into heat by members constituting the near-field transducer. The near-field transducer is covered with an alumina thin film having a low thermal conductivity, thereby trapping heat inside. The vicinity of the near-field transducer is heated to a very high temperature, reaching as high as 1000 degrees C. locally. Because of this high temperature, thermal deformation occurs in the vicinity of the near-field transducer. As a result of this thermal deformation, the thermally assisted magnetic recording head may collide with the disk, causing wear and contamination to the near-field transducer. Thus, there is a risk that the near-field transducer may be damaged. In addition, the change in the distance between the thermally assisted magnetic recording head and the disk due to the thermal deformation hampers stable magnetic recording.
A known example of such a thermally assisted magnetic recording device has been disclosed in Japanese Patent Application Laid-Open Publication No. 2009-43377.
In the thermally assisted magnetic recording device disclosed in Japanese Patent Application Laid-Open Publication No. 2009-43377, a temperature sensor is provided in the vicinity of a laser diode (hereinafter referred to as LD), which is a light source, to stabilize the intensity of the laser beam from the LD.
When a current flows through the LD, the temperature of the LD itself increases due to self heating. At this time, the intensity of the laser beam emitted from the LD varies depending on the temperature of the LD. Thus, the intensity of the laser beam reaching the near-field transducer varies during operation. As a result, the disk may not be heated constantly.
Thus, in Japanese Patent Application Laid-Open Publication No. 2009-43377, the temperature of the LD is measured by a temperature sensor to control the current flowing through the LD based on the measured temperature, in order to keep the intensity of the laser beam constant.